Movement of material underneath the slab or ejection of material from underneath the slab as a result of water pressure. Water accumulated underneath a PCC slab will pressurize when the slab deflects under load. This pressurized water can do one of the following:

  • Move about under the slab.
  • Move from underneath one slab to underneath an adjacent slab. This type of movement leads to faulting.
  • Move out from underneath the slab to the pavement surface. This results in a slow removal of base, subbase and/or subgrade material from underneath the slab resulting in decreased structural support.

Figure 1: Pumping in action.

Figure 2: Broken slabs.

Figure 3: Pumping damage.


Decreased structural support of the slab, which can lead to linear cracking, corner breaks and faulting.

Possible Causes

Water accumulation underneath the slab. This can be caused by such things as: a high water table, poor drainage, and panel cracks or poor joint seals that allow water to infiltrate the underlying material.


First, the pumping area should be repaired with a full depth patch to remove any deteriorated slab areas. Second, consideration should be given to using dowel bars to increase load transfer across any significant transverse joints created by the repair. Third, consideration should be given to stabilizing any slabs adjacent to the pumping area as significant amounts of their underlying base, subbase or subgrade may have been removed by the pumping. Finally, the source of water or cause of poor drainage should be addressed.